This invention relates to a system and method for color normalization of board images including images of whiteboards, blackboards and other surface media (herein referred to as xe2x80x9cboardsxe2x80x9d). More particularly, the invention is directed to normalizing colors of images of a board surface to eliminate the effects of variable illumination and, in the case of mosaic images, to eliminate visible seams between tiles. The background color is used to normalize the color of the pixels such that undesired artifacts arising from camera gain and uneven lighting are eliminated.
While the invention is particularly directed to the art of image processing and color normalization, and will thus be described with specific reference thereto, it will be appreciated that the invention may have usefulness in other fields and applications.
By way of background, boards are widely used to maintain hand drawn textual and graphic images on a xe2x80x9cwall sizexe2x80x9d surface. This medium offers certain properties that facilitate a variety of interactive work practices. However, a drawback to using a board is that information is not easily transferred to other media.
Accordingly, devices such as that disclosed in U.S. Pat. Nos. 5,528,290 and 5,581,637 were developed. With such devices, boards are scanned using a technique of image mosaicing, whereby high resolution images of large surfaces are obtained with low resolution imaging devices. When using mosaicing, several snapshots of different regions, or tiles, of the surface are assembled to form a larger composite image.
Undesired image artifacts can occur in image mosaicing, however, creating apparent seams in the final composite image. For example, image misalignment artifacts occur when the overlap regions of the adjacent image tiles do not properly align with one another. In addition, lightness and color artifacts are generated when the tiles line up properly but the intensity levels, contrast, or color balance of adjacent tiles are not matched.
The present invention provides a new and improved image processing method for color images which overcomes problems and difficulties associated with lightness and color artifacts. The system and method is applicable to single-snapshot (or tile) images as well as mosaic images comprised of a plurality of tiles.
A system and method are provided to normalize colors in an image of a board surface to eliminate effects of variable illumination and, in the case of mosaic images, to eliminate visible seams between tiles. The background color of the image is normalized so that artifacts are eliminated.
In one aspect of the invention, a board or surface image is input into the system via a video camera and a processor. Image arrays for each color channel are generated, and a determination is made whether pixels are background pixels or foreground pixels. Next, a background image array is generated and filtered for each color channel. The image arrays are then divided by a corresponding filtered background image array.
In another aspect of the invention, in an image mosaic of a whiteboard scene, normalization is performed for each image snapshot independently.
In another aspect of the invention, the mosaic images are reconstructed to form a final image.
Further scope of the applicability of the present invention will become apparent from the detailed description provided below. It should be understood, however, that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art.